Printed chemical mechanical polishing pad having particles therein

ABSTRACT

A method of fabricating a polishing layer of a polishing pad includes determining a desired distribution of particles to be embedded within a polymer matrix of the polishing layer. A plurality of layers of the polymer matrix is successively deposited with a 3D printer, each layer of the plurality of layers of polymer matrix being deposited by ejecting a polymer matrix precursor from a nozzle. A plurality of layers of the particles is successively deposited according to the desired distribution with the 3D printer. The polymer matrix precursor is solidified into a polymer matrix having the particles embedded in the desired distribution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/243,571, filed Aug. 22, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/511,057, filed Oct. 9, 2014, which claimspriority to U.S. Provisional Patent Application Ser. No. 61/899,754,filed Nov. 4, 2013, the entire disclosures of which are incorporated byreference.

TECHNICAL FIELD

This present invention relates to polishing pads used in chemicalmechanical polishing.

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a silicon wafer. A variety of fabrication processes requireplanarization of a layer on the substrate. For example, for certainapplications, e.g., polishing of a metal layer to form vias, plugs, andlines in the trenches of a patterned layer, an overlying layer isplanarized until the top surface of a patterned layer is exposed. Inother applications, e.g., planarization of a dielectric layer forphotolithography, an overlying layer is polished until a desiredthickness remains over the underlying layer.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier head. The exposed surface of thesubstrate is typically placed against a rotating polishing pad. Thecarrier head provides a controllable load on the substrate to push itagainst the polishing pad. A polishing liquid, such as slurry withabrasive particles, is typically supplied to the surface of thepolishing pad.

One objective of a chemical mechanical polishing process is polishinguniformity. If different areas on the substrate are polished atdifferent rates, then it is possible for some areas of the substrate tohave too much material removed (“overpolishing”) or too little materialremoved (“underpolishing”).

Conventional polishing pads include “standard” pads and fixed-abrasivepads. A standard pad has a polyurethane polishing layer with a durableroughened surface, and can also include a compressible backing layer. Incontrast, a fixed-abrasive pad has abrasive particles held in acontainment media, and can be supported on a generally incompressiblebacking layer. However, commercially available fixed-abrasive pads aregenerally limited to specific materials, e.g., cerium oxide.

Polishing pads are typically made by molding, casting or sinteringpolyurethane materials. In the case molding, the polishing pads can bemade one at a time, e.g., by injection molding. In the case of casting,the liquid precursor is cast and cured into a cake, which issubsequently sliced into individual pad pieces. These pad pieces canthen be machined to a final thickness. Grooves can be machined into thepolishing surface, or be formed as part of the injection moldingprocess.

In addition to planarization, polishing pads can be used for finishingoperations such as buffing.

SUMMARY

An end user of a chemical mechanical polishing apparatus typicallyobtains consumables, such as polishing pads and polishing slurry, fromone or more vendors. The polishing slurry typically contains asuspension of abrasive particles in a fluid. The fluid typicallyincludes additional chemistry to ensure that abrasive particles areproperly suspended in the fluid and do not form undesirableagglomerations of abrasive particles, which could result in scratchingor other defects and render the polishing slurry unsuitable forpolishing.

In order to lower cost of ownership for the end user, and to reducewaste disposal, the polishing pad and the abrasive particles can becombined into a single entity, by embedding the abrasive particles intothe pad itself. However, embedding particles into pads poses variousproblems. As a result, abrasive materials embedded in polishing padshave been limited to materials such as cerium oxides. Although aluminaabrasive particles have been proposed, a polishing pad with aluminaparticles has not been practical to commercialize. At least one problemin the manufacture of a polishing pad with alumina abrasive particleshas been the difficulty in suspending alumina abrasive particles inpolymers (e.g., thermoset polymer) used to fabricate the polishing pads.For example, suspensions of alumina abrasive particles in the polymersolutions are not uniformly distributed. The non-uniform distributionleads to agglomeration of the alumina abrasive particles, and theagglomeration leads to defects when the polishing pad is used topolished substrates.

A technique for manufacturing polishing pads that have differentabrasive particles embedded therein is to use a 3D printing process. Ina 3D printing process a thin layer of pad precursor, e.g., a powder orliquid precursor, is progressively deposited and fused or cured to forma full 3-dimensional polishing pad. The abrasive particles are thenselectively deposited within the printed layer of pad precursor.

In one aspect, a method of fabricating a polishing layer of a polishingpad, includes determining a desired distribution of particles to beembedded within a polymer matrix of the polishing layer. The methodincludes successively depositing a plurality of layers of the polymermatrix with a 3D printer, each layer of the plurality of layers ofpolymer matrix being deposited by ejecting a polymer matrix precursorfrom a nozzle, Successively depositing the plurality of layers includesdistributing the particles in the plurality of layers according to thedesired distribution with the 3D printer. The method includessolidifying the polymer matrix precursor to form a solidified polymermatrix having the particles embedded in the desired distribution.

Implementations can include one or more of the following features. Themethod may further include premixing the polymer matrix precursor withthe particles according to the desired distribution to form a mixturethat is ejected by the nozzle. The polymer matrix precursor may be aliquid thermoset polymer. The polymer matrix precursor may be a moltenthermoplastic polymer. The polymer matrix precursor may be ejected fromthe nozzle of a first printhead and the particles may be ejected fromthe nozzle of a second printhead. The particles may be made of materialselected from the group consisting of silica, ceramic, metal, metaloxide, and polymer. The silica may be fumed or colloidal. The particlesmay be alumina. The particles may be abrasive particles. The particlesmay further include reactive particles that undergo chemical reactionswhen the polishing layer is used for polishing. The particles may have ahollow core. The particles may have sizes of up to 1 millimeter, e.g.,less than 10 μm, e.g., less than 1 μm. The particles may be round,elongated or faceted. The polishing layer may include pores formed bythe hollow core of particles. Solidifying the polymer matrix precursormay include curing the polymer matrix precursor. Curing the polymermatrix precursor may include ultraviolet (UV) curing. Curing the polymermatrix precursor may include thermal curing. The thermal curing may bedone with a laser or an IR lamp. The polymer matrix precursor mayinclude a urethane monomer. The solidified polymer matrix may includepolyurethane, acrylate, epoxy, acrylonitrile butadiene styrene (ABS),polyetherimide, or polyamide. Solidifying the polymer matrix precursorincludes cooling the polymer matrix precursor. The desired distributionmay be a uniform distribution of the particles within the polymermatrix. The desired distribution may be a patterned distribution of theparticles within the polymer matrix. The polymer matrix precursor andparticles may be deposited to produce patterned surface features on asurface of the polishing pad. The patterned surface features may includeelongated grooves. The patterned surface features may include elevatedfeatures resembling buttons.

In another aspect, a polishing pad includes a polishing layer having apolymer matrix and a desired distribution of particles embedded withinthe polymer matrix. The desired distribution of particles includesdifferent distribution densities of the particles across the polishinglayer.

Implementations can include one or more of the following features. Thepolishing pad may include elongated grooves on a surface of thepolishing pad. The particles may have sizes of up to 1 millimeters,e.g., less than 10 μm, e.g., less than 1 μm. The particles may be round,elongated or faceted. The polymer matrix may include polyurethane,acrylate, an epoxy, acrylonitrile butadiene styrene (ABS),polyetherimide, or polyamide.

In another aspect, a method of fabricating a polishing layer of apolishing pad includes premixing a polymer matrix precursor withparticles to form a mixture. The polymer matrix precursor used tofabricate a polymer matrix of the polishing layer. The method includesagitating the mixture prior to ejecting the mixture from a nozzle of a3D printer and successively depositing a plurality of layers of thepolymer matrix with the 3D printer. Each layer of the plurality oflayers of polymer matrix being deposited by ejecting the polymer matrixprecursor from the nozzle. Successively depositing the plurality oflayers includes depositing the particles in the plurality of layers withthe 3D printer. The method includes solidifying the polymer matrixprecursor to form a solidified polymer matrix having the particlesembedded therein.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic cross-sectional side view of an example polishingpad.

FIG. 1B is a schematic cross-sectional side view of another examplepolishing pad.

FIG. 1C is a schematic cross-sectional side view of yet another examplepolishing pad.

FIG. 2 is a schematic side view, partially cross-sectional, of achemical mechanical polishing station.

FIG. 3A is a schematic cross-sectional side view illustrating anexemplary 3D printer used to fabricate a polishing pad.

FIG. 3B is a schematic cross-sectional side view illustrating anexemplary 3D printer used to fabricate a polishing pad.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1A-1C, a polishing pad 18 includes a polishing layer22. As shown in FIG. 1A the polishing pad can be a single-layer pad thatconsists of the polishing layer 22, or as shown in FIG. 1C the polishingpad can be a multi-layer pad that includes the polishing layer 22 and atleast one backing layer 20.

The polishing layer 22 can be a material that is inert in the polishingprocess. The material of the polishing layer 22 can be a plastic, e.g.,polyurethane, acrylate, epoxy, acrylonitrile butadiene styrene (ABS),polyetherimide, or polyamides. In some implementations the polishinglayer 22 is a relative durable and hard material. For example, thepolishing layer 22 can have a hardness of about 40 to 80, e.g., 50 to65, on the Shore D scale.

As shown in FIG. 1A, the polishing layer 22 can be a layer ofhomogeneous composition, or as shown in FIG. 1B the polishing layer 22can include abrasive particles 28 held in a matrix 29 of plasticmaterial, e.g., polyurethane, acrylate, epoxy, acrylonitrile butadienestyrene (ABS), polyetherimide, or polyamides. The abrasive particles 28are harder than the material of the matrix 29. The abrasive particles 28can be from 0.05 wt % to 75 wt % of the polishing layer. For example,the abrasive particles 28 can be less than 1 wt % of the polishing layer22, e.g., less than 0.1 wt %. Alternatively, the abrasive particles 28can be greater than 10 wt % of the polishing layer 22, e.g., greaterthan 50 wt %. The material of the abrasive particles can be a metaloxide, such as ceria, alumina, silica or a combination thereof,polymeric, inter-metallic or ceramics.

In some implementations, the polishing layer includes pores, e.g., smallvoids. The pores can be 50-100 microns wide.

The polishing layer 18 can have a thickness D1 of 80 mils or less, e.g.,50 mils or less, e.g., 25 mils or less. Because the conditioning processtends to wear away the cover layer, the thickness of the polishing layer22 can be selected to provide the polishing pad 18 with a usefullifetime, e.g., 3000 polishing and conditioning cycles.

On a microscopic scale, the polishing surface 24 of the polishing layer22 can have rough surface texture, e.g., 2-4 microns rms. For example,the polishing layer 22 can be subject to a grinding or conditioningprocess to generate the rough surface texture. In addition, 3D printingcan provide small uniform features, e.g., down to 200 microns.

Although the polishing surface 24 can be rough on a microscopic scale,the polishing layer 22 can have good thickness uniformity on themacroscopic scale of the polishing pad itself (this uniformity refer tothe global variation in height of the polishing surface 24 relative tothe bottom surface of the polishing layer, and does not count anymacroscopic grooves or perforations deliberately formed in the polishinglayer). For example, the thickness non-uniformity can be less than 1mil.

Optionally, at least a portion of the polishing surface 24 can include aplurality of grooves 26 formed therein for carrying slurry. The grooves26 may be of nearly any pattern, such as concentric circles, straightlines, a cross-hatched, spirals, and the like. Assuming grooves arepresent, then the polishing surface 24, i.e., the plateaus between thegrooves 26, can be about i.e., can be 25-90% of the total horizontalsurface area of the polishing pad 22. Thus, the grooves 26 can occupy10%-75% of the total horizontal surface area of the polishing pad 18.The plateaus between the grooves 26 can have a lateral width of about0.1 to 2.5 mm.

In some implementations, e.g., if there is a backing layer 20, thegrooves 26 can extend entirely through the polishing layer 22. In someimplementations, the grooves 26 can extend through about 20-80%, e.g.,40%, of the thickness of the polishing layer 22. The depth of thegrooves 26 can be 0.25 to 1 mm. For example, in a polishing pad 18having a polishing layer 22 that is 50 mils thick, the grooves 26 canhave a depth D2 of about 20 mils.

The backing layer 20 can be softer and more compressible than thepolishing layer 22. The backing layer 20 can have a hardness of 80 orless on the Shore A scale, e.g., a hardness of about have a hardness of60 Shore A. The backing layer 20 can be thicker or thinner or the samethickness as the polishing layer 22.

For example, the backing layer can be an open-cell or a closed-cellfoam, such as polyurethane or polysilicone with voids, so that underpressure the cells collapse and the backing layer compresses. A suitablematerial for the backing layer is PORON 4701-30 from Rogers Corporation,in Rogers, Conn., or SUBA-IV from Rohm & Haas. The hardness of thebacking layer can be adjusted by selection of the layer material andporosity. The backing layer can also be formed of natural rubber,ethylene propylene diene monomer (EPDM) rubber, nitrile, orpolychloroprene (neoprene). Alternatively, the backing layer 20 formedfrom the same precursor and have the same porosity as the polishinglayer, but have a different degree of curing so as to have a differenthardness.

Turning now to FIG. 2 , one or more substrates 14 can be polished at apolishing station 10 of a CMP apparatus. A description of a suitablepolishing apparatus can be found in U.S. Pat. No. 5,738,574, the entiredisclosure of which is incorporated herein by reference.

The polishing station 10 can include a rotatable platen 16 on which isplaced the polishing pad 18. During a polishing step, a polishing liquid30, e.g., abrasive slurry, can be supplied to the surface of polishingpad 18 by a slurry supply port or combined slurry/rinse arm 32. Thepolishing liquid 30 can contain abrasive particles, a pH adjuster, orchemically active components.

The substrate 14 is held against the polishing pad 18 by a carrier head34. The carrier head 34 is suspended from a support structure, such as acarousel, and is connected by a carrier drive shaft 36 to a carrier headrotation motor so that the carrier head can rotate about an axis 38. Therelative motion of the polishing pad 18 and the substrate 14 in thepresence of the polishing liquid 30 results in polishing of thesubstrate 14.

3D printing offers a convenient and highly controllable process forproducing polishing pads with abrasives embedded in specific locationswithin the polishing layer. Referring to FIG. 3A, at least the polishinglayer 22 of the polishing pad 18 is manufactured using a 3D printingprocess. In the manufacturing process, thin layers of material areprogressively deposited and fused. For example, droplets 52 of padprecursor material can be ejected from a nozzle 54 of a droplet ejectingprinter 55 to form a layer 50. The droplet ejecting printer is similarto an inkjet printer, but uses the pad precursor material rather thanink. The nozzle 54 translates (shown by arrow A) across a support 51.

For a first layer 50 a deposited, the nozzle 54 can eject onto thesupport 51. For subsequently deposited layers 50 b, the nozzle 54 caneject onto the already solidified material 56. After each layer 50 issolidified, a new layer is then deposited over the previously depositedlayer until the full 3-dimensional polishing layer 22 is fabricated.Each layer is applied by the nozzle 54 in a pattern stored in a 3Ddrawing computer program that runs on a computer 60. Each layer 50 isless than 50% of the total thickness of the polishing layer 22, e.g.,less than 10%, e.g., less than 5%, e.g., less than 1%.

The support 51 can be a rigid base, or be a flexible film, e.g., a layerof polytetrafluoroethylene (PTFE). If the support 51 is a film, then thesupport 51 can form a portion of the polishing pad 18. For example, thesupport 51 can be the backing layer 20 or a layer between the backinglayer 20 and the polishing layer 22. Alternatively, the polishing layer22 can be removed from the support 51.

In general, abrasive particles 23 are locally dispensed into polishinglayer while the polishing layer 22 is printed layer by layer. Localdispensing of the abrasive particles helps to avoid agglomeration.

Specifically, the abrasive particles 23 can be premixed with a liquidthermoset polymer precursor. Continuous agitation of the mixture of thethermoset polymer precursor and the abrasive particles preventsagglomeration of the particles, similar to apparatus used to homogenizeink pigments used in ink jet printers. In addition, the continuousagitation of the mixture ensures fairly uniform distribution of theabrasive particles in the precursor. This can result in a more uniformdistribution of particles through the polishing layer, which can lead toimproved polishing uniformity and can also help avoid agglomeration.

The premixed mixture is dispensed from a single nozzle (e.g., the nozzle54) according to a particular pattern. For example, the premixed mixturecan be uniformly dispensed to produce a homogeneous polishing layer 22having a uniform distribution of embedded abrasive particles throughoutthe polishing layer 22.

Alternatively, a separate printhead 57 having a nozzle 58, as shown inFIG. 3B, can be used to dispense pure liquid thermoset polymerprecursors (i.e., without any abrasive particles), while the premixedmixture is dispensed only at selected locations. These selectedlocations collectively form the desired printing pattern of the abrasiveparticles and can be stored as a CAD-compatible file that is then readby an electronic controller (e.g., the computer 60) that controls theprinter. Electronic control signals are then sent to the printer 55 todispense the premixed mixture only when the nozzle 54 is translated tothe position specified by the CAD-compatible file.

Alternatively, instead of using a liquid thermoset polymer precursor,the abrasive particles can be premixed with a molten thermoplastic. Inthis case, the mixture with abrasive particles is also continuouslyagitated prior to being dispensed. After the mixture is dispensed fromthe 3D printer according to a desired printing pattern, the moltenportion of the mixture cools and solidifies, and the abrasive particlesare frozen in place. The continuous agitation of the mixture ensuresfairly uniform distribution of the abrasive particles in the precursor.This can result in a more uniform distribution of particles through thepolishing layer, which can lead to improved polishing uniformity and canalso help avoid agglomeration

Similar to the case when liquid thermoset polymer precursor is used, thethermoplastic mixture can be uniformly dispensed to produce a uniformdistribution of abrasive particles across the entire polishing layer 22.Alternatively, the thermoplastic mixture containing the abrasiveparticles can be dispensed only at selected locations in the polishinglayer, according to a desired printing pattern of the abrasive particlesthat is stored as a CAD-compatible file and read by an electroniccontroller used to drive the printer 55.

Rather than dispensing abrasive particles in a suspension from thenozzle 54, abrasive particles can be dispensed directly in powder formfrom the nozzle 54, while a different printhead 57 is used to dispensethe pad polymer precursor. The polymer precursor is first dispensedbefore abrasive particles are dispensed into the deposited polymermaterial, and the mixture is then subsequently cured.

Although 3D printing is particularly useful to construct polishing padsusing abrasive particles, e.g., alumina, that would be prone toagglomeration, this approach can be used for other polishing particles.Thus, the abrasive particles can include silica, ceramic oxides, metalsand hard polymers.

The printheads can print particles that are either solid or particlesthat have a hollow core. The printhead can also dispense different typesof particles, some of which can undergo chemical reactions during CMPprocessing to produce desired changes on the layer of the substrate thatis being polished Examples of chemical reactions used in CMP processingfor polishing pad include chemical processes that occur within the basicpH range of 10-14 that involve one or more of potassium hydroxide,ammonium hydroxide and other proprietary chemical processes used bymanufactures of slurry. Chemical processes that occur within an acidicpH range of 2-5 involving organic acids such as acetic acid, citric acidare also used in CMP processing. Oxidization reactions involvinghydrogen peroxide are also examples of chemical reactions used in CMPprocessing. Abrasive particles can also be used only to providemechanically abrasive functions. The particles can have sizes up to 1millimeter, e.g., less than 10 μm, e.g., less than 1 μm, and theparticles can have different morphology, for example, the particles canbe round, elongated or faceted.

Pores within the polishing pad have conventionally been used to locallyretain slurry within the polishing pad. With the abrasive particlesbeing held by the matrix, it may no longer be necessary for thepolishing pad to contain pores. Pores can still be selectivelydistributed within the printed polishing pad by depositing hollowspheres at locations where pores are desired.

Solidification can be accomplished by polymerization. For example, thelayer 50 of pad precursor material can be a monomer, and the monomer canbe polymerized in-situ by ultraviolet (UV) curing. The pad precursormaterial can be cured effectively immediately upon deposition, or anentire layer 50 of pad precursor material can be deposited and then theentire layer 50 be cured simultaneously.

However, there are alternative technologies to accomplish 3D printing.Alternatively, the printer creates the polishing layer 22 by spreading alayer of powder that includes abrasive particles 23 as additives, andejecting droplets of a binder material onto the layer of powder

The 3D printing approach allows tight tolerances to be achieved in thedistribution of abrasive particles that are embedded in the polishinglayer due to the layer-by-layer printing approach. Also, one printingsystem (with printer 55 and computer 60) can be used to manufacture avariety of different polishing pads, simply by changing the patternstored in the 3D drawing computer program.

In some implementations, the backing layer 20 can also be fabricated bya 3D printing process. For example, the backing layer 20 and polishinglayer 22 could be fabricated in an uninterrupted operation by theprinter 55. The backing layer 20 can be provided with a differenthardness than the polishing layer 22 by using a different amount ofcuring, e.g., a different intensity of UV radiation.

In other implementations, the backing layer 20 is fabricated by aconventional process and then secured to the polishing layer 22. Forexample, the polishing layer 22 can be secured to the backing layer 20by a thin adhesive layer 28, e.g., as a pressure-sensitive adhesive.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,either the polishing pad, or the carrier head, or both can move toprovide relative motion between the polishing surface and the substrate.The polishing pad can be a circular or some other shape. An adhesivelayer can be applied to the bottom surface of the polishing pad tosecure the pad to the platen, and the adhesive layer can be covered by aremovable liner before the polishing pad is placed on the platen. Inaddition, although terms of vertical positioning are used, it should beunderstood that the polishing surface and substrate could be held upsidedown, in a vertical orientation, or in some other orientation.

Accordingly, other implementations are within the scope of the followingclaims.

What is claimed is:
 1. A polishing pad, comprising: a polishing layerhaving a planar polishing surface, the polishing layer comprising apolymer matrix; and a distribution of particles embedded within thepolymer matrix with first locations of the polishing layer correspondingto cured droplets of pure polymer precursor and second, differentlocations of the polishing layer corresponding to cured droplets ofpolymer precursor mixed with the particles such that the distribution ofparticles comprises different distribution densities of the particleslaterally across the polishing layer parallel to the planar polishingsurface, and wherein the first locations of the polishing layer and thesecond, different locations of the polishing layer form a pattern acrossthe polishing layer.
 2. The polishing pad of claim 1, wherein theparticles have sizes of up to 1 millimeter.
 3. The polishing pad ofclaim 1, wherein the polymer matrix comprises polyurethane, acrylate,epoxy, acrylonitrile butadiene styrene (ABS), polyetherimide, orpolyamides.
 4. The polishing pad of claim 1, wherein the particles areabrasive particles.
 5. The polishing pad of claim 4, wherein theparticles are made of a material selected from the group consisting ofsilica, ceramic, metal, and metal oxide.
 6. The polishing pad of claim1, wherein the particles include reactive particles that undergochemical reactions when the polishing layer is used for polishing. 7.The polishing pad of claim 1, wherein the particles have a hollow core,such that the polishing layer comprises pores formed by the hollow coreof particles.
 8. The polishing pad of claim 7, wherein the particles aremade of polymer.
 9. The polishing pad of claim 8, wherein the particleshave sizes of up to 1 millimeter.
 10. The polishing pad of claim 1,comprising surface features on a surface of the polishing pad.
 11. Thepolishing pad of claim 10, wherein the surface features compriseelongated grooves.